In automotive vehicle hydraulic brake systems, the brake mechanisms are actuated through a hydraulic circuit which includes a so-called master cylinder or actuator. The master cylinder, normally, includes two tandem arranged pistons which displace hydraulic fluid to respective brake circuits. Each piston is typically provided with a so-called center port or central compensation valve which operates to relieve pressure in the brake circuit when the brake pedal is released and to provide a supply of makeup fluid to the cylinder chambers for subsequent brake actuating cycles.
One longstanding problem associated with central or center port compensation valves for hydraulic brake master cylinders is related to the tolerances in the working parts of the master cylinder which can cause excessive brake pedal travel before the center port valves are closed and hydraulic pressure is applied to the brake circuits. Excessive brake pedal travel or so-called travel loss caused by delayed closing of the compensation valves is undesirable from the standpoint of brake operator reaction, as well as the fact that the pedal travel loss delays the application of braking effort on the vehicle.
Various efforts have been put forth toward controlling the center port compensation valve clearance or gap variation problem with a view to minimizing brake pedal travel loss. However, the present invention is believed to provide a superior solution to the problem by providing an improved compensation valve construction and an improved method of assembling the components of a brake master cylinder to reduce the valve clearance or valve gap variation and to minimize the amount of brake pedal travel required to initiate braking effort in a brake system using a master cylinder which includes the present invention.
The present invention provides an improved hydraulic brake master cylinder assembly including one or more central or center port compensation valves.
In accordance with one aspect of the invention, a hydraulic master cylinder assembly is provided with one or more center port compensation valves which include a clearance or gap between a valve closure member and a valve seat and which is set at the time of assembly of the master cylinder to minimize brake pedal travel loss during operation of the brake master cylinder.
In particular, a center port compensation valve is provided which includes a closure member which engages a compensation valve actuator pin by a stem part which is of variable length and which, in accordance with a method of the invention, is set to a predetermined length at the time of assembly of the master cylinder. The center port compensation valve is advantageously configured to include an elastomer closure member with an actuator stem comprising a shaft part and a sleeve part which is force fitted over the shaft part. The stem part may be set to a desired length at the time of assembly of the master cylinder and its component parts.
Thanks to the configuration of the center port compensation valve, excessive and varied valve movement between open and closed positions is eliminated to thereby minimize brake pedal or brake actuator travel loss during operation of a brake system including a master cylinder assembly in accordance with the invention.
The invention further contemplates the provision of a tandem master cylinder assembly including a primary piston and a secondary piston, each piston including a center port compensation valve in accordance with the invention. Each compensation valve is set to have a predetermined actuator stem length at the time of assembly of the master cylinder and its components using a method in accordance with the invention.
Still further, the invention contemplates a method for assembling a hydraulic brake master cylinder including one or more pistons slidable in a master cylinder bore, each piston including a central or center port compensation valve whose operating characteristics may be set at the time of assembly, thanks to the unique configuration of the compensation valve.
Those skilled in the art will further appreciate the above-noted advantages and superior features of the invention, together with other important aspects thereof upon reading the detailed description which follows in conjunction with the drawings.